Homogenous/homogeneous

Sir Edwin Ray Lankester (1847-1929), having gained first class honours in natural science at Oxford in 1868, returned in 1891 to take the Linacre chair of comparative anatomy, becoming one of the leading zoologists of his generation. Lankester’s works are cited a little over 300 times in the Oxford English Dictionary—an impressive tally. For comparison, the major novels of Thomas Hardy, Lankester’s almost exact contemporary, are cited about 700 times. But what distinguishes Lankester is his use of neologisms: in two thirds of the citations his is the first recorded use of the word. Sometimes he created a completely new word to describe a new phenomenon or to translate a foreign text; elsewhere he used existing words in new meanings or to derive new adjectives or verbs. The words that he is recorded as having used first include gonad, host (an animal or plant that harbours a parasite), musculature, proctodaeum, toxin, and homogenous.

Lankester introduced “homogenous” in an article in the Annals of Natural History (1870;6:34-43), in which he proposed that there were two different ways in which homology in organisms could arise: homogeny (through common ancestry) and homoplasty (through common environment). The suffix -geny probably originally derived from the triliteral root GEN in γέυεςισ (genesis, from γίγυεςθαι, gignesthai, to be born). The proper adjectival form is therefore -genetic, and indeed the title of Lankester’s paper was “On the use of the term Homology in modern Zoology; and the distinction between Homogenetic and Homoplastic agreements.” However, in the text he perversely used two different adjectives, homogenous and homogenetic. His reasons for choosing one or the other are not clear, although he tended to use “homogenous” when describing structures that have homogeny, a common genetic origin, and “homogenetic” when qualifying another noun—for example, “homogenetic agreement.”

Now take homogeneous, an older word than homogenous (the earliest citation in the OED comes from Milton). If two things are homogeneous they are congruous, alike in constitution, of uniform nature or character throughout. A population is homogeneous if its members have some common characteristic. A tissue is homogeneous if it is composed of similar cells. In homogeneous equations the sum of the indices in each term is the same—for example, x³ – x²y + xy² – y³ = 0. In the Iliad we read (13:354) that Zeus and Poseidon were of the same stock, òμοσ γέυοσ (homos genos); perhaps Lankester had this in mind when he coined “homogenous.” But the corresponding adjective òμογευήσ (homogenes) became “homogeneus” in scholastic Latin. And in English this became “homogeneous,” by conflation of -eus with another suffix, -ous, which came from the Latin suffix -osus, meaning full of, giving the word a different meaning from its Greek roots.

So homogenous and homogeneous have distinct meanings. But homogenous is nowadays virtually always mistakenly used to mean homogeneous. For instance, a Medline search of the titles and abstracts of papers published throughout the world in 1997 shows 170 instances of “homogenous,” in almost all cases incorrectly used to mean “homogeneous.” In 1348 other papers “homogeneous” was used. In contrast, since 1965 (when the database starts) the British Medical Journal has not used the word homogenous in any title or abstract; the one case in which it appeared to do so (1975;3:18-20) turned out to be a misprint in Medline!

Homogenous is probably mistaken for homogeneous because the two words look alike and because homogenous is not nowadays commonly used in its original meaning. “Homogenize,” which means to make homogeneous, may have exacerbated the confusion.

But don’t confound the two. After all, you don’t think that knowing all the answers to the questions in the variety of Trivial Pursuit known as “Genus” makes you a genius—do you?

Footnotes